Method of forming bumps on a wafer utilizing a post-heating operation, and an apparatus therefore

ABSTRACT

A bump forming apparatus which carries out a temperature control of a type different from the conventional art in forming bumps to a semiconductor wafer, and a bump formation method executed by the bump forming apparatus are provided. A bonding stage, a load and transfer device and a control device are provided. A wafer, after having bumps formed thereon, is held by the load and transfer device and arranged above the bonding stage through control by the control device, so that a temperature drop of the wafer is controlled. Accordingly, generation of troubles such as a crack because of thermal stress and the like can be prevented to even compound semiconductor wafers sensitive to a temperature change.

This application is a Divisional application of Ser. No. 09/719,768filed Dec. 18, 2000, which is currently now U.S. Pat. No. 6,787,391.

TECHNICAL FIELD

The present invention relates to a bump forming apparatus for formingbumps on semiconductor wafers, and a bump formation method carried outby the bump forming apparatus.

BACKGROUND ART

In recent years, electronic components have been made more and morecompact in accordance with miniaturization of devices, e.g., portablephones and the like on which the electronic components are mounted.Thus, there is a bump forming apparatus for this purpose which formsbumps to electrode portions at each circuit formation part on asemiconductor wafer without separating the circuit formation part fromthe semiconductor wafer. The bump forming apparatus of this kindincludes a carry-in device for taking out a semiconductor wafer beforebumps are formed thereto from a first storage container where thesemiconductor wafers without bumps are stored, a second storagecontainer for storing wafers with the bumps formed, a bonding stagewhere wafers without bumps are placed and heated generally to about250-270° C. so as to join the electrode portions and bumps, a carry-outdevice for storing the wafers after the bumps are formed thereon intothe second storage container, and a transfer device for transferring thewafers from the carry-in device to the bonding stage and from thebonding stage to the carry-out device.

Meanwhile, as a SAW (Surface Acoustic Wave) filter used in theaforementioned portable phones and the like, there are somesemiconductor wafers having a substrate of the wafer not formed ofsilicon as in the prior art but formed of quartz, or a compoundsemiconductor wafer such as lithium tantalum, lithium niobium, galliumarsenide or the like. Although the compound semiconductor wafer of thistype is heated as well to approximately 150° C. at maximum in formingthe bumps, it is necessary for the heating and cooling speed of thecompound semiconductor wafer to be lowered in comparison with theconventional silicon wafer. Unless the cooling is carried out slowly,the compound semiconductor wafer is accompanied by a pyroelectric effectthereby breaking circuits, or the wafer is thermally deformed to crackin some cases.

As such, a bump forming apparatus for forming bumps to the compoundsemiconductor wafers needs a different way of temperature control fromthe control in the conventional bump forming apparatus which forms bumpsto silicon wafers.

The present invention has for its object to provide a bump formingapparatus which executes temperature control different from the priorart before and after forming bumps to semiconductor wafers, and a bumpformation method carried out by the bump forming apparatus.

SUMMARY OF THE INVENTION

In order to accomplish the above and other objects, a bump formationmethod is provided according to a first aspect of the present inventionfor forming bumps onto electrodes of a circuit formed to a semiconductorwafer. In the bump formation after bonding the bumps on thesemiconductor wafer by practical heating for bump formation and method,before storing the semiconductor wafer in a storage container, apost-heating operation in which a temperature drop of the semiconductorwafer is controlled is performed on the semiconductor wafer.

In a second aspect of the present invention, a preheating operation isperformed on the semiconductor wafer before the semiconductor wafer ispractically heated in addition to the bump formation method of the firstaspect.

In a bump formation method according to a fifth aspect of the presentinvention, before the bump bonding is carried out after thesemiconductor wafer is placed on a bonding stage which heats thesemiconductor wafer to a temperature for bump bonding in the practicalheating, a temperature difference between a temperature at a side of astage contact face of the semiconductor wafer in contact with thebonding stage and a temperature at a side of a circuit formation face ofthe semiconductor wafer opposite to the stage contact face may becontrolled in addition to the bump formation method of the first aspect.Thus, the semiconductor wafer placed on the bonding stage is maintainedwithin a warpage non-generation temperature range in which a warpage ofthe semiconductor wafer is restricted to a level not obstructing thebump formation.

A bump forming apparatus provided according to a third aspect of thepresent invention has a bonding stage where a semiconductor wafer isplaced and which practically heats the semiconductor wafer to atemperature for bump bonding necessary to form bumps on electrodesformed to a circuit of the semiconductor wafer. In addition, a bumpforming head is placed above the bonding stage for forming the bumpsonto the electrodes of the semiconductor wafer, and a load and transferdevice is provided for putting and removing the semiconductor wafer onthe bonding stage. Furthermore, a post-heating device is provided forcooling the semiconductor wafer based on a temperature drop control tothe semiconductor wafer after bumps are bonded on the practically heatedsemiconductor wafer.

In a bump forming apparatus according to a fourth aspect of the presentinvention, a preheating device can be additionally provided for the bumpforming apparatus of the third aspect for carrying out a preheatingoperation on the semiconductor wafer before the semiconductor waferplaced on the bonding stage is heated to the temperature for bumpbonding.

A bump forming apparatus according to a sixth aspect of the presentinvention may have a wafer temperature control device added to the bumpforming apparatus of the third aspect. Before the bump bonding iscarried out after the semiconductor wafer is placed on the bondingstage, the wafer temperature control device controls the temperaturedifference between a temperature at a side of a stage contact face ofthe semiconductor wafer placed on the bonding stage in contact with thebonding stage and a temperature at a side of a circuit formation face ofthe semiconductor wafer opposite to the stage contact face so that thetemperature difference is within a warpage non-generation temperaturedifference range where a warpage of the semiconductor wafer isrestricted to a level not obstructing the bump formation.

According to the bump formation method in the first aspect and the bumpforming apparatus in the third aspect of the present invention, thepost-heating device executes the post-heating operation for controllinga temperature drop of the wafer after bumps are formed on the wafer.Thus, generation of troubles such as a circuit break due to apyroelectric effect, a crack by thermal deformation and the like can beprevented even when compound semiconductor wafers sensitive to atemperature change are handled.

In the bump formation method of the second aspect and the bump formingapparatus of the fourth aspect of the present invention, the preheatingdevice is further provided in addition to the post-heating device,thereby heating the semiconductor wafer while controlling a temperaturerise of the wafer before bumps are formed on the wafer. Thus, even whencompound semiconductor wafers sensitive to a temperature change arehandled, generation of troubles such as a circuit break by apyroelectric effect, a crack by thermal deformation and the like can befurther prevented.

In the bump formation method of the fifth aspect and the bump formingapparatus of the sixth aspect of the present invention, the wafertemperature control device is additionally set to execute temperaturecontrol on the semiconductor wafer placed on the bonding stage tosuppress a warpage of the semiconductor wafer to a level not obstructingthe bump formation. Thus, the semiconductor wafer can be maintained in anearly flat state even at high temperatures, e.g., 200-250° C., so thatbumps can be formed on the semiconductor wafer at the high temperatures.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and features of the present invention willbecome clear from the following description taken in conjunction withthe preferred embodiments thereof with reference to the accompanyingdrawings, in which:

FIG. 1 is a perspective view of a bump forming apparatus according to anembodiment of the present invention;

FIG. 2 is a perspective view of a transfer device shown in FIG. 1;

FIG. 3 is a perspective view of a load and transfer device shown in FIG.1;

FIG. 4 is a perspective view of a modification of the load and transferdevice of FIG. 3;

FIG. 5 is a plan view of the load and transfer device of FIG. 3;

FIG. 6 is a sectional view of a clamp mechanism of the load and transferdevice of FIG. 3;

FIG. 7 is a flow chart showing operations in a bump formation methodcarried out by the bump forming apparatus of FIG. 1;

FIG. 8 is a graph of various temperature rise curves at the time ofpreheating in step 5 of FIG. 7;

FIG. 9 is a graph of various temperature rise curves at the preheatingin step 5 of FIG. 7;

FIG. 10 is a graph of temperature drop curves in step 8 or 9 of FIG. 7;

FIG. 11 is a sectional view of a modified example of a carry-out deviceshown in FIG. 1;

FIG. 12 is a sectional view of a modified example of the carry-outdevice shown in FIG. 1;

FIG. 13 is a sectional view of a modified example of the carry-outdevice shown in FIG. 1;

FIG. 14 is a sectional view of a projecting part included in thecarry-out device shown in FIGS. 11-13;

FIG. 15 is a diagram of a modified example of the load and transferdevice of FIG. 1;

FIG. 16 is a perspective view of a temporary holding member included ina modified example of the bump forming apparatus of FIG. 1;

FIG. 17 is a block diagram of a modified example of the bump formingapparatus of FIG. 1;

FIG. 18 is a perspective view of the bump forming apparatus in FIG. 1 inwhich a heating air blow device constitutes a wafer temperature controldevice;

FIG. 19 is a diagram of a state in which a quartz semiconductor wafer iswarp on a bonding stage; and

FIG. 20 is a flow chart of operation in step 6 of FIG. 7 in the casewhere the bump forming apparatus of FIG. 1 is provided with the wafertemperature control device.

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

A bump forming apparatus according to an embodiment of the presentinvention and a bump formation method carried out by the bump formingapparatus will be described with reference to the drawings, in whichlike parts are designated by like reference numerals. A bump formingapparatus 101 according to this embodiment shown in FIG. 1 isappropriate to process the earlier mentioned compound semiconductorwafers and will be discussed in the following description in relation toforming bumps on the compound semiconductor wafers. However, an objectto be processed by the apparatus is not limited to the compoundsemiconductors, and the apparatus can also process conventional siliconwafers. In such a case, wafers on which bumps are formed are heated upto approximately 250-270° C. as described before. The bump formingapparatus 101 has a first storage container 205 for storing compoundsemiconductor wafers 201 in layers before bumps are formed, and a secondstorage container 206 for storing compound semiconductor wafers 202 inlayers after bumps are formed (that is, the apparatus is a doublemagazine type). However, the apparatus is not restricted to this typeand can be formed as a so-called single magazine type with one storagecontainer for storing both the compound semiconductor wafers 201 withoutbumps and the compound semiconductor wafers 202 with bumps.

The bump forming apparatus 101 is fundamentally not different from thebump forming apparatus of the prior art. That is, the bump formingapparatus 101 roughly consists of one bonding stage 110, one bumpforming head 120, transfer devices 130, one load and transfer device140, lifting devices 150 connected to the above storage containers 205,206 for moving up and down the storage containers 205, 206 respectively,and a control device 180. As will be described later in relation to theoperation of the bump forming apparatus 101, the apparatus is greatlydifferent from the conventional apparatus in its operation under thecontrol of the above control device 180 so as to effectuate temperaturecontrol to particularly prevent compound semiconductor wafers fromcracking or the like. Each of the above parts constituting the apparatuswill be described below.

The bonding stage 110 has thereon the compound semiconductor waferbefore bumps are formed (referred to simply as “pre-wafer” hereinbelow)201, and heats the pre-wafer 201 to a temperature for bump bonding whichis necessary for forming bumps onto electrodes of circuits formed on thepre-wafer 201.

The bump forming head 120 is a known device for forming bumps on theelectrodes of the pre-wafer 201 loaded on the bonding stage 110 andheated to the temperature for bump bonding. The bump forming head notonly has a wire supply part 121 for supplying a gold wire as a materialfor the bumps, but also has a bump formation part for melting the goldwire thereby forming a ball and pressing the molten ball to theelectrode, and an ultrasonic wave generation part for applyingultrasonic waves to the bump at the time of the above pressing. The thusconstituted bump forming head 120 is set on an X, Y-table 122 having,for example, ball screw structures movable in X, Y-directions orthogonalto each other on a plane, and moved in the X, Y-directions by the X,Y-table 122 so that a bump can be formed on each of the electrodes ofthe fixed pre-wafer 201.

The bump forming apparatus 101 has transfer devices 130 of two kinds. Acarry-in device 131 comprising one of the transfer devices is a devicefor taking out the pre-wafer 201 from the first storage container 205,while a carry-out device 132 comprising the other of the transferdevices is a device for transferring and storing the compoundsemiconductor wafer after bumps are formed (referred to simply as“post-wafer” below) 202 to the second storage container 206. Morespecifically, as indicated in FIG. 2, the above carry-in device 131 andthe above carry-out device 132 are arranged side by side in the Xdirection. The devices are moved independently of each other by movableparts 134 a including rodless cylinders 134 fixed to a frame 133 whilebeing guided by guide members 135 secured to the frame 133. As shown inFIG. 1, between the carry-in device 131 and carry-out device 132 is thebonding stage 110. Therefore the carry-in device 131 moves between thefirst storage container 205 and bonding stage 110, and the carry-outdevice 132 moves between the bonding stage 110 and second storagecontainer 206.

The carry-in device 131 has, as shown in FIG. 2, a move-side holdingmember 1311 and a fixed-side holding member 1312 which are bothconnected to a supporting member 1314. The pre-wafer 201 can be loadedon the move-side holding member 1311. The move-side holding member 1311can be moved in a diametrical direction of the pre-wafer 201 by adriving part 1313 set to the supporting member 1314 and having an aircylinder. The driving part 1313 moves the move-side holding member 1311in a direction away from the fixed-side holding member 1312, namely, inan open direction. On the other hand, moving the move-side holdingmember 1311 in a direction approaching the fixed-side holding member1312 (i.e., in a close direction) is done by an urging force of anelastic member such as a spring or the like. The move-side holdingmember 1311 is moved in the open direction to move the carry-in device131 by the movable part 134 a of the rodless cylinder 134 to a positioncorresponding to the pre-wafer 201 in the first storage container 205.Then the holding member 1311 is moved in the close direction, wherebythe pre-wafer 201 is caught by positioning rollers 1315 attached to themove-side holding member 1311 and position regulation rollers 1316attached to the fixed-side holding member 1312. The first storagecontainer 205 is attached to a first lifter 151 constituting the liftingdevice 150. The first lifter 151 moves the first storage container 205up and down so that the pre-wafer 201 is at a position where the wafercan be taken out by the carry-in device 131. The pre-wafer 201 taken outfrom the first storage container 205 by the carry-in device 131 is heldby the load and transfer device 140. The above-described operation ofthe carry-in device 131 is controlled by the control device 180.

The carry-out device 132 has a loading member 1321 for loading thereonpost-wafer 202 transferred from the load and transfer device 140. Theloading member 1321 has a plurality of suction holes 1322 for suckingand holding the post-wafer 202. The holes 1322 formed in an arraycorresponding to nearly central parts of loaded post-wafer 202 areconnected to a suction device 1323 controlled by the control device 180.In one feature of this embodiment, the carry-out device 132 is providedwith a plurality of air blast holes 1324 formed adjacent to the suctionholes 1322 for jetting a gas for controlling the cooling of thepost-wafer 202. These air blast holes 1324 are connected to an air blastdevice 1325 controlled in operation by the control device 180.Post-wafer 202 loaded on the loading member 1321 can be cooled moreslowly than in the case of natural cooling by the temperature-controlledgas (i.e., temperature-controlled air in the embodiment which is jettedfrom the air blast holes 1324 by the air blast device 1325). The airjetted out from the air blast holes 1324 is discharged outside theloading member 1321 through discharge grooves 1326 formed in the loadingmember 1321. The air blast holes 1324 are opened to the dischargegrooves 1326, while the suction holes 1322 are opened to a surface 1321a of the loading member 1321 to which the post-wafer 202 comes incontact. Since the air jetted from the air blast holes 1324 passes thedischarge grooves 1326, the problem in that the post-wafer 202 isblasted off the loading member 1321 because of the jetted air iseliminated. The number of air blast holes 1324, discharge grooves 1326and suction holes 1322 is not limited to the number indicated in thedrawing.

The above air blast holes 1324, air blast device 1325 and dischargegrooves 1326 may also be arranged on a member of the carry-in device 131where wafer 201 is loaded, loaded (i.e., to the move-side holding member1311 in the embodiment).

The load and transfer device 140 shifts the pre-wafer 201 from theabove-described carry-in device 131 to the bonding stage 110, and shiftsthe post-wafer 202 from the bonding stage 110 to the carry-out device132. As shown in FIG. 3, the load and transfer device has one holdingpart 141 for holding wafer 201, 202, a drive part 142 having a ballscrew structure driven by a motor 1421 for moving the holding part 141in the X-direction, and a move part 143 for moving the holding part 141up and down in a thicknesswise direction of the held wafer 201, 202. Theholding part 141 can be disposed immediately above each of the bondingstage 110, move-side holding member 1311 and fixed-side holding member1312 of the carry-in device 131, and loading member 1321 of thecarry-out device 132, thereby transferring the wafer 201, 202 among thebonding stage, carry-in device 131 and carry-out device 132 through theup, down movement by the move part 143. The load and transfer device 140constituted as above is controlled in operation by the control device180. As is indicated in FIG. 3, the load and transfer device 140 may beequipped with a temperature measuring device 1419 which can measure atemperature of the held wafer 201, 202 in a noncontact state (withoutcontacting the wafer) and send the measured result to the control device180.

As shown in FIGS. 3 and 5, the holding part 141 includes, according toone of the features of the embodiment, a pair of first clamp members1411-1, 1411- (referred to as a “first clamp member 1411” collectivelyin some cases) and a pair of second clamp members 1412-1, 1412-2(referred to as a “second clamp member 1412” collectively in some cases)for holding the wafers 201, 202 respectively in two directionsorthogonal to each other in each plane of the wafers 201, 202. Theholding part 141 also has a driving mechanism 1413 for bringing thefirst clamp members 1411-1, 1411-2 and second clamp members 1412-1,1412-2 away from each other and close to each other. Two units of clampmechanisms 1414 are arranged at positions opposite to each other betweenthe first clamp member 1411-1 and first clamp member 1411-2 of the firstclamp member 1411, and clamp mechanisms 1414 of one unit are arranged atpositions opposite to each other between the second clamp member 1412-1and second clamp member 1412-2 of the second clamp member 1412. Each ofthese clamp mechanisms 1414 has, as is clear in FIG. 6, a housing 1415,a pin 1416 penetrating the first clamp member 1411, second clamp member1412 in a thicknesswise direction thereof which moves slidably in thehousing 1415 along an axis direction thereof, a holding metal fitting1417 fitted to an end part of the pin 1416 in a state so as to berotatable in a direction about an axis of the pin 1416 and having a dropprevention flange 1418 for the wafer 201, 202, and a spring 1420installed in the housing 1415 for urging the pin 1416 in the axisdirection. The clamp mechanisms 1414 are set at 6 points via an almostequal distance along the periphery of the wafer 201, 202 held by thefirst clamp member 1411 and second clamp member 1412, so that theholding metal fittings 1417 hold the wafer 201, 202 at the 6 points.

The embodiment is provided with not only the first clamp member 1411,but also with the second clamp member 1412, thereby holding the wafer201, 202 at 6 points spaced apart at almost equal distances as mentionedabove. Accordingly, application of a dynamically biased stress to thewafer 201, 202, and moreover, application of a thermally biasedtemperature distribution to the wafer are eliminated. Since the holdingmetal fittings 1417 hold the wafer 201, 202 while maintaining contactwith the periphery of the wafer 201, 202, especially the post-wafer 202in a heated state, heat is transmitted from the post-wafer 202 to theholding metal fittings 1417. However the holding metal fittings 1417apply no thermally biased temperature distribution to the post-wafer 202even when holding the post-wafer 202, because the holding metal fittings1417 are arranged at 6 points spaced apart at almost equal distances. Inthe arrangement of the embodiment in which both the first clamp member1411 and the second clamp member 1412 are provided and also the wafer201, 202 is held at 6 points via the almost equal distance, generationof troubles such as the earlier-discussed cracks or the like to thecompound semiconductor wafers which are sensitive to a temperaturechange and need to be cooled more slowly than silicon wafersparticularly after bumps are formed thereon is effectively prevented.

Furthermore, since the pins 1416 are movable in the axis direction, theholding metal fittings 1417 can move in the axis direction as well. Forinstance, the heated post-wafer 202 is sometimes accompanied withwarpage because of the heat when held on the bonding stage 110. Thepost-wafer 202 returns from the above deflect state to the original flatstate while being cooled when held by the holding metal fittings 1417.The holding metal fittings 1417 can move in the axis direction followingthe restoration of the post-wafer 202 and, therefore, the clampmechanisms 1414 prevent generation of a stress to the wafer 202.

The driving mechanism 1413 for bringing the first clamp members 1411 andsecond clamp members 1412 close to or away from each other respectivelyhas a cylinder 14131 as a driving source and a second clamp membermoving mechanism 14132 for moving each of the second clamp members1412-1, 1412-2 synchronously with the movement of the clamp member1411-2. The second clamp member moving mechanism 14132 has a structurein which a first member 14133 coupled at one end to the first clampmember 1411-2 is coupled to a second member 14135 rotatable in acircumferential direction of a rotational center shaft 14134 via a jointpart 14136. The first member 14133 moves in accordance with the movementof the first clamp member 1411-2 in the X-direction, and consequentlythe second member 14135 rotates, thereby moving the second clamp member1412 in the Y-direction.

The driving mechanism 1413 operates in a manner as describedhereinbelow. In order to separate the first clamp member 1411 and secondclamp member 1412 to receive the wafer 201, 202, the cylinder 14131operates to extend an output shaft 14137 in the X-direction until thefirst clamp member 1411-1 coupled to the output shaft 14137 butts with astopper in the X-direction. The first clamp member 1411-2 moves in theX-direction as the movement of the first clamp member 1411-1 is stoppedby the stopper. In accordance with this movement of the first clampmember 1411-2, the second clamp member 1412 moves in the Y-direction bythe action of the second clamp member moving mechanism 14132 asdescribed above. In the case where the first clamp member 1411 andsecond clamp member 1412 are to be separated from each other asdescribed above, the first clamp member 1411-1 moves first, then thefirst clamp member 1411-2 and the second clamp member 1412 movesimultaneously. On the other hand, in the case where the first clampmember 1411 and second clamp member 1412 are to be brought close to eachother so as to hold the wafer 201, 202, the first clamp member 1411-2and second clamp member 1412 move at the same time due to the action ofthe cylinder 14131, and then the first clamp member 1411-1 moves.

A time difference is set as above in operation timing between the firstclamp member 1411-2 and second clamp member 1412, and the first clampmember 1411-1, which prevents a force from acting at one time upon thewafer 201, 202 particularly when the wafer 201, 202 is held.

According to the embodiment, the above-described bonding stage 110, theload and transfer device 140, and the control device 180 constitute apreheating device for the pre-wafer 201 and a post-heating device.Although one control device 180 controls the operation of the preheatingdevice and post-heating device in the present embodiment, a secondcontrol device 180-2 and a first control device 180-1 may be provided tocorrespond to the preheating device and the post-heating device,respectively, for controlling the devices. In addition, the carry-outdevice 132 from which the temperature-controlled gas is jetted throughair blast holes 1324 formed in the loading member 1321 by the air blastdevice 1325, or a modified example of the carry-out device with aninsulating material on the loading member which will be described laterand shown in FIGS. 11-13 may be included in the post-heating device.

Alternatively, each group having the bonding stage 110, the load andtransfer device 140, and the control device 180 can be constructed asthe above preheating device and the post-heating device, respectively.In this constitution, each of control devices for the preheating deviceand the post-heating device may be integrated to one. Further in theconstitution, the carry-out device 132 to which thetemperature-controlled gas is jetted or the carry-out device with theinsulating material may be similarly included in the post-heatingdevice.

Operation of the bump forming apparatus 101 in the embodimentconstituted as described hereinabove will be depicted below. Theoperation is controlled by the control device 180 which carries out atleast a post-heating operation for cooling the post-wafer 202 whilecontrolling the temperature before the post-wafer 202 with bumps formedat the bonding stage 110 is stored in the second storage container 206,which is a characteristic operation of the embodiment to be detailedlater. Although the wafers 201, 202 in the following description are3-inch compound semiconductor wafers, needless to say, a type and a sizeof the wafers are not restricted to this.

The first lifter 151 operates to move up or down the first storagecontainer 205 so that the pre-wafer 201 is arranged at a take-outposition where the wafer can be taken out from the first storagecontainer 205 by the carry-in device 131. As shown in FIG. 7, in a step(indicated by “S” in the drawing) 1, the carry-in device 131 moves tothe first storage container 205, and the move-side holding member 1311and the fixed-side holding member 1312 of the carry-in device 131 holdthe pre-wafer 201. In a next step 2, the held wafer 201 is taken outfrom the first storage container 205 and transferred. In a followingstep 3, the holding part 141 of the load and transfer device 140 movesto a position above the pre-wafer 201 held by the carry-in device 131,the move part 143 of the load and transfer device 140 drives to lowerthe holding part 141, and the cylinder 14131 of the holding part 141drives to separate the first clamp member 1411 and separate the secondclamp member 1412. The cylinder 14131 operates to bring the first clampmember 1411 and the second clamp member 1412 close together, therebyholding the pre-wafer 201. In a succeeding step 4, the holding part 141moves up and the drive part 142 shifts the holding part 141 to aposition above the bonding stage 110.

In the embodiment, before the pre-wafer 201 is placed on the bondingstage 110, the pre-wafer 201 is preheated while being held by theholding part 141 (step 5). If the pre-wafer 201 at normal temperature isimmediately placed on the bonding stage 110 and heated to a temperaturefor bump bonding which is approximately 150° C. at maximum, the wafer(if it is the compound semiconductor wafer sensitive to a temperaturechange) will probably develop a circuit destruction or theabove-mentioned crack because of the pyroelectric effect. Thus, thewafer is preheated for avoiding this.

As a concrete way of preheating, in the embodiment, the pre-wafer 201held by the holding part 141 is arranged above the bonding stage 110which is already heated to nearly the temperature for bump bonding, in anoncontact state opposite to the bonding stage 110, so that the wafer isheated by radiant heat from the bonding stage 110. A temperature-risecontrolling of the pre-wafer 201 in the preheating method can becontrolled by controlling at least either a size of a gap between thebonding stage 110 and the pre-wafer 201, or the period of time duringwhich the pre-wafer 201 is at the position. A combination of the gapsize and the time also enables various kinds of control as shown inFIGS. 8 and 9. FIG. 8 shows a case in which the gap size and arrangementtime are not changed during a preheating operation. In other words, thisgraph shows a temperature rise curve in the case of a one-stagepreheating type in which the pre-wafer 201 is placed on the bondingstage 110 at a time point when the pre-wafer 201 reaches an equilibriumstate of a temperature of the pre-wafer 201 and is then heated to thetemperature for bump bonding. On the other hand, FIG. 9 shows a case inwhich the gap size and arrangement time are changed during thepreheating operation, namely, the temperature rise curve in the case ofa multiple-stage preheating type. In FIGS. 8 and 9, t1, t2, t3, t4, t5are times used for the preheating and, T1, T2, T3, T4 are temperaturesin the equilibrium state in the preheating operation. T is thetemperature for bump bonding. The temperature rise curve represented by1001 corresponds to this embodiment and has a temperature increase ratein which it takes approximately 90 seconds to raise the temperature ofthe wafer to 80° C.

A condition for selecting an appropriate control among the varioustemperature rise controls is selected on the basis of at least one of amaterial of the semiconductor wafer and a thickness of the semiconductorwafer. The material of the semiconductor wafer means, for example, atype of the wafer (that is, whether the wafer is a silicon wafer orcompound semiconductor wafer, and further the kind of compound of thesemiconductor wafer).

Patterns of the various temperature rise controls may be stored as aprogram for the preheating into a memory part of the control device 180beforehand, so that the control device 180 can automatically select atemperature rise control appropriate for the preheating on the basis ofat least one of the material and thickness of the semiconductor waferinput to the control device 180. Also the temperature rise control maybe carried out on the basis of information on an actual temperature ofthe pre-wafer 201, which information is supplied to the control device180 from the temperature measuring device 1419 set on the holding part141.

The preheating is executed by using the heat of the bonding stage 110 inthe embodiment. The preheating is not restricted to this, however, and aheating device for the preheating may be separately provided.

The operation can shift from step 4 directly to a step 6 describedbelow, although the step 5 is executed in the embodiment.

In the step 6, similar to the conventional bump forming apparatus, theload and transfer device 140 places the pre-wafer 201 onto the heatedbonding stage 110, whereby the pre-wafer 201 is heated to thetemperature for bump bonding. Then, the bump forming head 120, whilebeing moved by the X, Y-table 122 to bump formation points, forms bumpsonto the wafer 201.

After the bumps are formed at all required points, the load and transferdevice 140 holds the post-wafer 202 on the bonding stage 110 in a step7. After the step 7 (i.e., in either a step 8 or a step 9), thepost-heat operation which is one of the characteristic features of theembodiment is carried out. If the post-wafer 202 at the temperature forbump bonding is immediately placed on the loading member 1321 at thenormal temperature of the carry-out device 132, the heat is transmittedfrom the post-wafer 202 to the loading member 1321, thereby possiblybreaking the semiconductor wafer when the semiconductor wafer is acompound semiconductor wafer which is sensitive to the temperaturechange, or bringing about similar trouble. For preventing this, thewafer 202 is cooled while a temperature drop is controlled. As a way ofconducting the post-heating according to the embodiment, the post-wafer202 is arranged above the bonding stage 110 by the load and transferdevice 140, similar to the above preventing (in step 8). Alternatively,the post-wafer 202 is positioned by the load and transfer device 140 ata cooling position other than above the bonding stage 110 (for instance,above the loading member 1321 of the carry-out device 132, which iscarried out in the step 9). In any way, the post-wafer 202 is preventedfrom immediately contacting the loading member 1321 having the normaltemperature, and the temperature drop of the post-wafer 202 is delayed.The post-heating operation is not limited to these methods and can becarried out in various manners as described later.

In the post-heating operation executed in the step 8, either or both ofthe gap size and arrangement time are changed in the same manner as inthe preheating operation executed in the step 5, whereby the temperaturedrop is controlled to represent, for example as shown in FIG. 10, atemperature drop curve nearly inverse to the temperature rise curveshown in FIGS. 8 and 9. A graph indicated by 1002 is the temperaturedrop curve when the gap size and arrangement time are not changed duringthe post-heating operation, similar to the aforementioned one-stagepreheating type. On the other hand, a graph designated by 1003 is thetemperature drop curve when the gap size and arrangement time arechanged during the post-heating operation, similar to the multi-stagepreheating type. t6, t7 are times spent for the post-heating, and T5, T6are temperatures in an equilibrium state in the post-heating operation.T0 is the normal temperature. The post-wafer 202 is moved to the loadingmember 1321 of the carry-out device 132 at a point in time after theabove time t6, t7 has passed.

Similar to the preheating operation, the control of the temperature dropis selected from among various kinds on the basis of at least either ofthe material and the thickness of the wafer 201, 202.

Also similar to the preheating operation, patterns of various kinds oftemperature drop controls may be stored beforehand as a program for thepost-heating in the memory part of the control device 180, so that thetemperature drop control appropriate to the post-heating isautomatically selected by the control device 180 based on at least oneof the material and thickness of the semiconductor wafer input to thecontrol device 180. Alternatively, the temperature drop control may beperformed on the basis of information regarding an actual temperature ofthe post-wafer 202 which is supplied from the temperature measuringdevice 1419 of the holding part 141 to the control device 180.

The post-heating is executed in the embodiment by using heat from thebonding stage 110, but the post-heating is not limited to this. Aheating device for the post-heating may be set separately.

Since the heat emitted from the bonding stage 110 will not act in thepost-heating operation carried out in the step 9 in contrast to step 8,the temperature of the post-wafer 202 drops faster in step 9 than in thestep 8. However, the cooling speed is slow because of the absence ofheat transmission to the loading member 1321 in comparison with the casewhen the wafer is placed onto the loading member 1321 immediately afterbumps are formed, and consequently troubles such as the above-referredcrack or the like are eliminated even from the above compoundsemiconductor wafer.

Herein a relationship between rates of the temperature rise andtemperature drop in the above preheating operation and post-heatingoperation, and the material and thickness of the semiconductor wafer,will be described.

Silicon and quartz semiconductor wafers can be relatively rapidly heatedand cooled as compared with wafers of materials described below. Forcompound semiconductor wafers of lithium tantalum and lithium niobium, atemperature change rate of 50° C./min or lower is preferred to preventcracking during both the heating and the cooling, and in order to makesure of the operation of the electric circuit, a temperature change rateof 3° C./min or lower is preferred. The operation of the electriccircuit is sufficiently ensured even at a rate exceeding the above 3°C./min. The temperature rise rate of about 50° C./10 sec is allowed insome cases, whereas the temperature drop control is severer incondition. Although not determined at present, the above condition ofthe lithium tantalum and lithium niobium semiconductor wafers maysupport a condition for semiconductor wafers of gallium arsenide.

A clear relationship between the thickness and the temperature rise rateand temperature drop rate has not been clearly established at present.However, the wafer when held by the holding part of the transfer andload device is easier to deflect by a holding force of the holding partbecause the wafer is thinner. Therefore, a small thickness is considereddisadvantageous.

Although either step 8 or step 9 should be carried out (and theembodiment carries out step 9), an executed process is not limited tothis. In other words, step 8 and then step 9 may be sequentially carriedout in this order depending on the material and thickness. Furthermore,since the temperature-controlled air can be sent by the air blast device1325 as described earlier at the loading member 1321 of the embodiment,it is possible to preliminarily raise the loading member 1321 to notlower than the normal temperature by the air, or the temperature drop ofthe post-wafer 202 placed on the loading member 1321 can be delayed bythe air. In such structure, the step 7 may be followed by a step 10 tobe depicted below depending on the material and thickness of thesemiconductor wafer.

The above-described arrangement of blowing the temperature-controlledair from the loading member 1321 can also prevent generation of problemssuch as cracking or the like in the compound semiconductor wafers.

Since the temperature drop of the wafer 202 is controllable by blowingthe temperature-controlled air as indicated above, the wafer 202 can bemoved onto the loading member 1321 without waiting for the temperatureequilibrium state thereof by the post-heating. Therefore, if theapparatus has only one load and transfer device 140, the load andtransfer device 140 can be more quickly freed from the operation ofholding the wafer 202 during the post-heating, so that a lead time isshortened.

In the step 10 after step 8 or step 9, the post-wafer 202 is moved fromthe load and transfer device 140 to the loading member 1321 of thecarry-out device 132.

In step 11, the post-wafer 202 is transferred by the carry-out device132 in the second storage container 206. In a step 12, the post-wafer202 is stored by the carry-out device 132 to the second storagecontainer 206 set by the second lifter 152 to a height whereat thecontainer can store the post-wafer 202. The operation from the abovestep 10 through step 12 is equal to the operation in the conventionalart.

According to the bump forming apparatus 101 and bump formation method ofthe embodiment as described hereinabove, the pre-wafer 201 is notdirectly heated by the bonding stage 110 to the temperature for bumpbonding, but is preheated in the preheating operation while thetemperature rise is controlled. Troubles such as a circuit break causedby a pyroelectric effect, cracking because of thermal deformation andthe like are prevented even when compound semiconductor wafers sensitiveto the temperature change are handled. Moreover, the post-wafer 202 isnot directly moved onto the loading member 1321 (at thenormal-temperature) of the carry-out device 132 when at the temperaturefor bump bonding, but is cooled in the post-heating operation while thetemperature drop is controlled. Therefore, generation of troubles suchas the above circuit break, cracking or the like is eliminated even whenthe compound semiconductor wafers are handled.

As modified embodiments of the above-described bump forming apparatus101, the following constitutions may be adopted.

In the above-described embodiment, the loading member 1321 of thecarry-out device 132 is formed of a metallic sheet. A thermal insulatingmaterial, specifically a resin material, may be applied to a contactpart of the loading member for contacting the post-wafer 202, as incarry-out devices 251-253 shown in FIGS. 11-13, whereby cooling of thepost-wafer 202 which is higher than the normal temperature can bedelayed.

More specifically, in the carry-out device 251 in FIG. 11, a thermalinsulating material 2512 is set on the metallic loading member 2511,thereby preventing the loading member 2511 from being in direct contactwith the post-wafer 202. The thermal insulating material 2512 as a resinmaterial makes it difficult to transmit heat from the post-wafer 202 tothe loading member 2511. Furthermore, the thermal insulating material2512 has projections 2513 so that the post-wafer 202 is brought in pointcontact with the thermal insulating material 2512, thereby furtherobstructing the heat transmission. In the constitution as describedabove, the temperature drop of the post-wafer 202 can be delayed incomparison with the case in which the post-wafer 202 is directly placedon the metallic loading member 1321.

The carry-out device 252 in FIG. 12 has an air layer 2523 formed betweenthe loading member 2521 and a thermal insulating member 2522 in additionto the structure of the above carry-out device 251. The heattransmission from the insulating material 2522 to the metallic loadingmember 2521 is easy to block by forming the air layer 2523 having a heatinsulation effect. Therefore, the temperature drop of the post-wafer 202can be delayed more than in the above carry-out device 251.

The reason for setting the thermal insulating material on the metallicloading member as in the carry-out device 251 and carry-out device 252is to provide a smooth load face of the thermal insulating materialwhere the post-wafer 202 is loaded by forming the smooth face on themetallic loading member to which a plane processing can be done easier.However, if the load face of the thermal insulating material can be madesmooth easier, the loading member for the post-wafer 202 can be formedonly of the thermal insulating material 2531 as in the carry-out device253 shown in FIG. 13.

Since the speed for cooling the post-wafer 202 can be delayed in thecarry-out devices 251-253 with the thermal insulating material asdescribed above, step 8 or 9 may or may not be carried out.

As indicated in FIG. 14 exemplifying the carry-out device 251, aprojection 2513 is set with gaps 2515 in the thermal insulating material2512 and loading member 2511. When the post-wafer 202 moves in anorthogonal direction with respect to a thicknesswise direction thereofafter being loaded on the carry-out device 251, the projection 2513 canmove together with the post-wafer 202 in the orthogonal direction at thegaps. If the projection is fixed while the post-wafer 202 moves, theprojection and the post-wafer 202 rub each other thereby unfavorablydamaging the post-wafer 202. However, the possibility of damage iseliminated by designing the projection 2513 to move with the post-wafer202 in the same direction as above.

As shown in the drawing, the projection 2513 is provided in the thermalinsulating material 2512 via the gap 2515 also in the thicknesswisedirection of the post-wafer 202. Consequently, the projection 2513 canalso move in the thicknesswise direction of the wafer 202.

The projection 2513 alone may be formed of a material different from thematerial of the thermal insulating material 2512, 2522, 2531.

In order to thermally insulate the pre-wafer 201 and post-wafer 202better than in the present embodiment, the load and transfer device 140may be provided with a heat insulation device. FIG. 15 shows a load andtransfer device 261 obtained by mounting a heat insulation device 262 onthe load and transfer device 140.

The heat insulation device 262 has a member 2621 for covering, and adriving part 2624. The member 2621 for covering is a heat insulationmember for the wafer 201, 202, including an upper cover 2622 and a lowershutter 2623 which are arranged in the thicknesswise direction of thewafer 201, 202 and are arranged to cover the holding part 141 having thefirst clamp member 1411 and second clamp member 1412. The lower shutter2623 is constituted of two lower portions 2623-1, 2623-2 opened rightand left by the driving part 2624 in a diametrical direction withrespect to the wafer 201, 202 held by the holding part 141. Each of thelower shutter portions 2623-1, 2623-2 has a plurality of openings 2625formed to penetrate the lower shutter 2623-1, 2623-2 so that the heatfrom the bonding stage 110 easily acts upon the wafer 201, 202.

Because of the presence of the heat insulation device 262 constituted asdescribed above, when the wafer 201, 202 is disposed above the bondingstage 110 in the earlier-described step 5 and step 8 with the lowershutter 2623 closed and the wafer 201, 202 held, the heat from thebonding stage 110 stays in the member 2621 for covering. As a result,the wafer 201, 202 can be insulated thermally.

Moreover, the heat insulation device 262 can be equipped with a heatinsulation assisting device 263 for blowing a temperature-controlled gas(to assist heat insulation for the wafer 201,202) onto the wafer 201,202 held within the member 2621 for covering. In the present embodiment,the gas is nitrogen gas, which is guided by a pipe 2631 to flow along asurface of the wafer 201, 202 and is blown to the wafer 201, 202. Theentire wafer 201, 202 can be kept at a uniform temperature by theblowing of the gas. Oxidation of electrodes formed on the wafer 201, 202can be also prevented when the nitrogen gas or an inert gas is blown.

For shortening the lead time in the bump formation process as well aspreventing generation of troubles such as breakage of the wafer 201,202, an arrangement to be described below can be provided in addition tothe constitution of the above embodiment and its modified example.

More specifically, while the load and transfer device 140 of theembodiment has only one holding part 141 as discussed above, two holdingparts 144-1, 144-2 may be provided as in a load and transfer device 144of FIG. 4. Then the holding parts 144-1, 144-2 may be drivenindependently so that, for example, the holding part 144-1 loads andtransfers pre-wafer 201, and the holding part 144-2 loads and transfersthe post-wafer 202. A temperature measuring device 1419 is provided foreach of the holding parts 144-1, 144-2.

Each of operations for loading and transferring the pre-wafer 201 andpost-wafer 202 can be shared by the holding parts respectively in theabove constitution, so that the lead time can be shortened.

In the case of only one load and transfer device 140, a temporaryholding member 271 can be provided on at least one of the carry-indevice 131 and the carry-out device 132 as shown in FIG. 16. Supposingthat the temporary holding member 271 provided on the carry-in device131 is a first temporary holding member 271-1, and the temporary holdingmember 271 provided on the carry-out device 132 is a second temporaryholding member 271-2, in the example of the carry-in device 131, thefirst temporary holding member 271-1 is formed in a U-shape so as tohold the loading member 1321 and is moved up and down in thethicknesswise direction of the wafer 202 placed on the loading member1321 by a driving device 272 controlled in operation by the controldevice 180. When the first temporary holding member 271-1 is provided asdescribed above, the wafer 201 can be delivered between the loadingmember 1321 and the first temporary holding member 271-1, while theloading member 1321 can take out the next pre-wafer 201. The lead timecan be accordingly shortened. The operation and effect as describedabove are equally achieved in the case of the second temporary holdingmember 271-2.

As indicated in FIG. 17, in a bump forming apparatus 301 of theso-called single magazine type with only one storage container 302 forthe wafers 201, 202, there are included a temporary holding member 303with a heater in addition to the above temporary holding member, theabove temporary holding member 304, a transfer device 305 for sendingthe wafers 201, 202 in and out of the storage container 302, and a loadand transfer device 306. According to the arrangement, for example,while the pre-wafer 201 taken out by the transfer device 305 is placedand preheated by the temporary holding member 303 with the heater, thenext pre-wafer 201 can be taken by the freed transfer device 305, andthe post-wafer 202 can be moved by the load and transfer device 306 tothe temporary holding member 304 from the bonding stage 110. Sinceoperations can be executed concurrently with the use of the temporaryholding member, the lead time can be shortened even in the singlemagazine type. In the above constitution, the temporary holding member303 with the heater is preferably provided with an appropriate coolingdevice because the temporary holding member 303 is required to be cooledto nearly the normal temperature after preheating before the nextpre-wafer 201 is loaded.

Second Embodiment

A semiconductor wafer having a semiconductor circuit formed on, e.g., aquartz substrate (referred to as a “quartz semiconductor wafer”hereinbelow) has a problem yet to be solved as shown below, although thecompound semiconductor wafer primarily exemplified in the foregoingdescription is less troubled. The quartz semiconductor wafer discussedhere has a diameter of 3 inches and a thickness of 0.3-0.35 mm, but isnot limited to this size.

From a view point of facilitating bump formation onto the semiconductorwafer, the temperature for bump bonding is preferably as high aspossible (for instance, approximately 250-270° C. for silicon wafers,and approximately 150° C. for lithium tantalum wafers). The quartzsemiconductor wafer is not an exception. However, a phenomenon belowtakes place in experiments conducted by the applicant, in which thepreheated quartz semiconductor wafer is placed on the bonding stage setat various temperatures and heated to a temperature for bump bonding.Even when the bonding stage is gradually heated with a temperature riserate of 5° C./min, a quartz semiconductor wafer 211 is warped asillustrated in FIG. 19 when the bonding stage reaches approximately 250°C. Specifically, the wafer 211 is warped when a stage contact face 211 bof the quartz semiconductor wafer 211 in contact with the bonding stagereaches the above temperature of the bonding stage, i.e., approximately250° C. Also, if a temperature difference between the bonding stage andthe quartz semiconductor wafer 211 immediately before being placed onthe bonding stage is approximately 50° C., the quartz semiconductorwafer 211 is warped as indicated in FIG. 19. The warpage is broughtabout if the quartz semiconductor wafer is rapidly heated (e.g., heatedat a rate of 20° C./min) even when the temperature difference is notlarger than 50° C.

A concrete value of the warpage, i.e., a size I in FIG. 19, isapproximately 2 mm.

The quartz semiconductor wafer 211 in a state in which the wafer iswarped cannot be sucked onto the bonding stage, and bumps cannot beformed on the warped quartz semiconductor wafer 211. If the warpedquartz semiconductor wafer 211 is forcibly sucked onto the bondingstage, the quartz semiconductor wafer 211 cracks.

A cause of the warpage is considered to result substantially from thephysical properties of the quartz semiconductor wafer 211, but isdirectly due to a nonuniformity in the temperature of the quartzsemiconductor wafer 211 in the thicknesswise direction. In other words,although the stage contact face 211 b of the quartz semiconductor wafer211 is rapidly heated when placed on the bonding stage, a temperaturerise speed of a circuit formation face 211 a of the quartz semiconductorwafer 211 opposite to the stage contact face 211 b is lower as comparedwith the stage contact face 211 b, thereby bringing about a temperaturedifference between the stage contact face 211 b and circuit formationface 211 a. The temperature difference creates the warpage of the quartzsemiconductor wafer.

In the embodiment, a wafer temperature control device 160 is provided asshown in FIG. 1 or 18, which controls the temperature difference betweenthe circuit formation face 211 a and the stage contact face 211 b withina warpage non-generation temperature range where the warpage of thequartz semiconductor wafer 211 placed on the bonding stage 110 isrestricted to an amount not impeding the bump formation to the loadedquartz semiconductor wafer 211, specifically, 50 μm in the embodiment.The above amount of warpage corresponds to the size represented by “I”in FIG. 19 in a state before the warped quartz semiconductor wafer 211is sucked to the bonding stage 110. When bumps are actually formed, theabove 50 μm becomes not larger than approximately 20 μm because of thesuction operation. The wafer temperature control device 160 heats thecircuit formation face 211 a of the quartz semiconductor wafer 211placed on the bonding stage 110, or cools the stage contact face 211 bso as to keep the temperature difference in the warpage non-generationtemperature range. The warpage non-generation temperature range iswithin approximately 20° C. based on the result of the experiments.

In one form of heating the circuit formation face 211 a, a heating airblow device 161 is provided on the wafer temperature control device 160as shown in a detailed manner in FIG. 18. The heating air blow device161 is arranged at a position so as not to interfere with the operationof the bump forming head 120 in a back side of the bonding stage 110.The heating air blow device 161 blasts heating air having a temperaturewhich accommodates the temperature difference within the warpagenon-generation temperature range to an entire area or almost the entirearea of the circuit formation face 211 a of the quartz semiconductorwafer 211 placed on the bonding stage 110. For example, the bondingstage 110 is set to 200° C. and the heating air of 200° C. is sent outfor approximately 30 seconds from the heating air blow device 161.

The position at which the heating air blow device 161 is installed isnot limited to the above position and, e.g., can also be arranged at afront side of the bonding stage 110. The heating air blow device 161 isconnected to the control device 180, and the temperature, a blowingtime, a volume, a velocity of the heating air, and similar propertiesare controlled on the basis of a relationship to the temperature of thebonding stage 110.

Meanwhile, a cooling air supply device 162 may be arranged in a way tocool the stage contact face 211 b in the wafer temperature controldevice 160 as clearly indicated in FIG. 18. A plurality of suction holes111 are formed in the bonding stage conventionally for sucking thesemiconductor wafer, and the junction holes 111 communicate with asuction device 113 through an air passage 112. The cooling air supplydevice 162 is connected to the air passage 122 and supplies cooling airvia the air passage 122 to an entire area or almost the entire area ofthe stage contact face 211 b. Since projections 114 for positioning andsupporting the placed semiconductor wafer are formed on the bondingstage 110, the quartz semiconductor wafer 211 is prevented from droppingfrom the bonding stage 110 as a result of the supply of the cooling airby the cooling air supply device 162. The cooling air supply device 162is connected to the control device 180, and a temperature, a supplytime, a volume, a velocity, and similar properties of the cooling airare controlled on the basis of a relationship to the temperature of thebonding stage 110. In the embodiment, when the bonding stage 110 is setto 200° C., the cooling air is sent out from the cooling air supplydevice 162 for about 20 seconds. The cooling air temperature immediatelyafter being sent out from the cooling air supply device 162 and beforereaching the stage contact face 211 b is 185° C.

As a way for correcting the warpage, normally, setting the heating airblow device 161 for heating the circuit formation face 211 a which islower in temperature than the stage contact face 211 b is preferred.However, in the case of setting the cooling air supply device 162,conveniently, since the existing air passage 112 can be utilized and aninstallation position thereof can be selected with a high degree offlexibility, the cooling air supply device 162 is more convenient thanthe heating air blow device 161.

Operation of the wafer temperature control device 160 constituted asdescribed above will be discussed with reference to FIG. 20. Theoperation shown in FIG. 20 corresponds to the heating and bondingoperation of the quartz semiconductor wafer 211 in step 6 of FIG. 7. Thecooling air supply device 162 is employed by way of example of the wafertemperature control device 160 in the embodiment.

In the present embodiment, the bonding stage 110 is set to 200° C. Asdescribed before, since the temperature difference between the bondingstage 110 and the quartz semiconductor wafer 211 placed on the bondingstage 110 should be within approximately 50° C., the preheating iscarried out in step 5 to the quartz semiconductor wafer 211. Thepreheating in this embodiment is conducted in two stages according tothe embodiment as described with reference to FIG. 8. The quartzsemiconductor wafer 211 is first raised to 100° C. and then heated to150° C. The circuit formation face 211 a and stage contact face 211 b ofthe quartz semiconductor wafer 211 become equal in temperature at apoint in time when the preheating is completed.

In step 61, the quartz semiconductor wafer 211 is placed by the holdingpart 141 of the load and transfer device 140 onto the bonding stage 110.The quartz semiconductor wafer 211 is subjected to practical heating instep 62. Although the quartz semiconductor wafer 211 starts to be warpedbecause the stage contact face 211 b is quickly heated subsequent to theabove placement on the bonding stage, a step 63 is executedsimultaneously with the step 62. That is, the cooling air is supplied bythe cooling air supply device 162 to the whole area or almost the wholearea of the stage contact face 211 b of the quartz semiconductor wafer211 for about 20 seconds, so that a temperature increase ratio of thestage contact face 211 b is suppressed. The temperature differencebetween the circuit formation face 211 a and the stage contact face 211b is thus kept within the warpage non-generation temperature range inwhich the warpage of the quartz semiconductor wafer 211 is restricted tothe amount of warpage of the wafer which does not obstruct formation ofbumps to the quartz semiconductor wafer 211. Even if warpage isgenerated, the warpage is corrected and therefore the warpage of thequartz semiconductor wafer 211 is kept in the above described amount.According to the above operation, the quartz semiconductor wafer 211 isheated to the temperature for bonding (i.e., 200°) which is the settemperature of the bonding stage 110 in the embodiment.

In step 64, after being heated to the temperature for bonding, thequartz semiconductor wafer 211 is sucked onto the bonding stage 110 bythe action of the suction device 113, and bumps are formed on thecircuit formation part by the bump forming head 120.

The operation following the step 7 is carried out afterwards.

According to the embodiment as described above, the warpage of thequartz semiconductor wafer 211 is restricted during the practicalheating within the amount of the warpage of the wafer whereby theformation of bumps is not hindered. Therefore, the quartz semiconductorwafer 211 can be heated to high temperatures (e.g., 200-250°) with thewarpage being kept to the above amount, and thus the bumps can be formedon the quartz semiconductor wafer 211.

As described above, although the cooling air supply device 162 uniformlysupplies the cooling air to the entire area or nearly the entire area ofthe stage contact face 211 b, the temperature, a feed amount, or similarcharacteristics of the air may be changed based on a position on thestage contact face 211 b from a view point of more effectivelypreventing generation of warpage. For instance, a cooling air supplydevice for supplying the cooling air to a central part of the quartzsemiconductor wafer 211, and a cooling air supply device for supplyingthe cooling air to another part may be provided, and the cooling air tothe central part may be lowered in temperature or increased in amount ascompared to the cooling air supplied to the other part.

The quartz semiconductor wafer 211 is described by way of example in theforegoing description. However, the second embodiment is not limited tothis wafer and useful to semiconductor wafers using a substance whichpoorly transmits heat and greatly changes a thermal expansioncoefficient depending on temperatures.

Although the present invention has been fully described in connectionwith the preferred embodiments thereof with reference to theaccompanying drawings, it is to be noted that various changes andmodifications are apparent to those skilled in the art. Such changes andmodifications are to be understood as included within the scope of thepresent invention as defined by the appended claims unless they departtherefrom.

1. A bump forming apparatus comprising: a bonding stage for supporting asemiconductor wafer and for heating the semiconductor wafer to atemperature for forming bumps on electrodes on a circuit of thesemiconductor wafer; a bump forming head for forming the bumps on theelectrodes of the semiconductor wafer; a load and transfer device forplacing the semiconductor wafer on and removing the semiconductor waferfrom said bonding stage; a controller programmed to operate said bondingstage and said load and transfer device so as to perform a post-heatingoperation on the semiconductor wafer after the bumps are formed on thesemiconductor wafer to thereby control a temperature drop of thesemiconductor wafer, said controller being operable to control thepost-heating operation on the semiconductor wafer by controlling saidload and transfer device and said bonding stage so that thesemiconductor wafer is positioned by said load and transfer device at acooling position above said bonding stage while said bonding stage isheated to the temperature for forming the bumps such that thesemiconductor wafer does not contact said bonding stage when in thecooling position; and a wafer temperature control device programmed tooperate a temperature difference between a temperature at a bondingstage-contact face of the semiconductor wafer and a temperature at acircuit formation face of the semiconductor wafer opposite to thebonding stage-contact face before the bump formation is performed andafter the semiconductor wafer is positioned on said bonding stage, saidwafer temperature control device being operable to control thetemperature difference to be within a warpage non-generation temperaturedifference range so that a warpage of the semiconductor wafer isrestricted to a level not obstructing the bump formation.
 2. The bumpforming apparatus of claim 1, wherein said wafer temperature controldevice is operable to control the temperature difference by heating thecircuit formation face of the semiconductor wafer placed on said bondingstage.
 3. The bump forming apparatus of claim 2, wherein said wafertemperature control device is operable to heat the circuit formationface by supplying heating air to the circuit formation face of thesemiconductor wafer, the heating air having a temperature formaintaining the temperature difference within the warpage non-generationtemperature difference range.
 4. The bump forming apparatus of claim 1,wherein said wafer temperature control device is operable to control thetemperature difference by cooling the bonding stage-contact face of thesemiconductor wafer placed on said bonding stage.
 5. The bump formingapparatus of claim 4, wherein said wafer temperature control device isoperable to cool the bonding stage-contact face by supplying cooling airto the bonding stage-contact face of the semiconductor wafer, thecooling air having a temperature for maintaining the temperaturedifference within the warpage non-generation temperature differencerange.
 6. The bump forming apparatus of claim 1, wherein said wafertemperature control device is operable to maintain the temperaturedifference within a warpage non-generation temperature difference rangeof 20° C.
 7. The bump forming apparatus of claim 1, wherein thesemiconductor wafer comprises a quartz-based wafer.